My best guess is that the ABS was not designed to be used over and over and over again on a regular basis. I trail brake a lot and while it doesn't cause the ABS to fully engage, I suspect it does some sort of "work" every time I use the brakes to get the car to rotate a little.
The one I'm putting in this weekend will be #4 including the original.
My car is generally getting thrashed hard, or getting driven somewhere it will be thrashed hard.
This is why I'm a fanatic when it comes to maintenance.
